The invention relates to an incandescent electric lamp having a lamp envelope, an incandescent filament arranged within said lamp envelope, current conductors extending through said envelope connected to respective ends of said filament for supplying electric current thereto, and support means between said filament ends for supporting said filament with respect to said lamp envelope.
Such a lamp is known from U.S. Pat. No. 3,600,053, (Smith) which discloses a single ended tungsten halogen cycle lamp having a quartz glass lamp envelope with a pinch seal at one end and a tipped-off exhaust tubulation at the opposite end. The filament is "U" shaped, and is comprised of two symmetrical filament parts. One end of each filament part is connected to a respective current conductor adjacent the pinch seal. The filament is secured to the tubulated end of the envelope by a wire insert secured in the tubulation which has ends that are inserted in the other ends of the two filament parts near the tubulation.
GB 1,178,062 and U.S. Pat. No. 3,544,188 (Danko et al) also disclose lamps having a wire support member fixing the filament to the envelope. These lamps have a support wire with one end secured in the exhaust tubulation and a loop or hook at the other end holding the filament. Additional support for the filament in some lamps is provided by a quartz-glass bridge fixed to the current conductors at a location between the filament ends and the pinch seal. Instead of a support wire fixed in the tubulation, another known lamp construction employs a quartz-glass bridge and a frame wire extending therefrom which supports the filament remote from the pinch seal.
Other types of incandescent lamps also employ wire filament supports which engage the wall of the lamp envelope. Elongate tubular incandescent lamps, such as the photocopier lamp of U.S. Pat. No. 5,001,388, commonly employ a plurality of spiral wire supports which hold the filament and spiral outwards to engage the wall of the envelope and support the filament on the lamp axis.
In the above lamps, the wire filament supports are undesirable because they increase the number of lamp parts, complicate lamp assembly and parts handling, and generally increase the cost of the lamp. The looped or hooked supports are detrimental to lamp life because they sufficiently lower the temperature of the filament to subject the filament to halogen attack at the areas where they contact the filament. The filaments are also susceptible to breakage from physical shock because of the high temperature gradient of the filament next to the support points and the small contact area between the loop or hook of the wire support and the filament. Additionally, in single ended lamps which employ a bridge, the lamp envelope must be long enough to accommodate the bridge, and provide clearance between the bridge and the pinch seal, the coil, and the upper support. Thus, the lamp envelope must be longer than necessary for enclosing the filament.
Accordingly, it is the object of the invention to provide an incandescent lamp of the kind described in the opening paragraph with improved filament support means which overcome the above-mentioned disadvantages.